The Zanos Lab recently presented groundbreaking findings from the PROUD clinical trial at the NeuroGeorgia 2025 International Neuroscience Conference. The presentation, delivered by the PROUD research team, showcased the first randomized controlled trial results examining ketamine’s antidepressant efficacy and underlying neurobiological mechanisms in individuals with opioid use disorder during abstinence maintenance. This pioneering work addresses a critical gap in treatment options for a highly vulnerable population facing both addiction and mental health challenges.

Opioid use disorder represents a global public health crisis, with depression co-occurring in approximately thirty to fifty percent of individuals receiving opioid substitution treatment. This comorbidity substantially worsens treatment outcomes, increases relapse risk, and elevates suicide mortality. Despite this critical clinical need, evidence-based pharmacological interventions addressing depression in opioid use disorder populations remain limited, particularly during the vulnerable abstinence maintenance phase when conventional antidepressants demonstrate delayed onset and modest efficacy. While ketamine has demonstrated rapid antidepressant effects in treatment-resistant depression, its therapeutic potential and mechanistic profile in opioid use disorder populations with comorbid depression remained unclear prior to the PROUD study.

The PROUD project represents the first double-blind, placebo-controlled, randomized clinical trial specifically examining ketamine’s efficacy, safety, and neurobiological mechanisms in this population. The study enrolled participants with opioid use disorder under supervised abstinence maintenance who presented with comorbid depressive symptoms, aged eighteen to sixty-five years. Participants received six intravenous infusions of ketamine at a dose of 0.5 mg/kg or saline placebo, administered over forty minutes across a two-week period. Depression severity was assessed using the Montgomery-Åsberg Depression Rating Scale at multiple time points including baseline, forty to eighty minutes post-infusion, twenty-four hours, two weeks, three months, and nine months post-infusion. The study incorporated comprehensive assessments of potential mechanistic factors, including heart rate variability as an index of autonomic and emotional regulation, stress biomarkers including plasma cortisol, adrenocorticotropic hormone, noradrenaline and adrenaline, synaptic plasticity markers such as brain-derived neurotrophic factor, and electroencephalography recordings to assess cortical neuronal activity changes at baseline, during infusion, and post-infusion.

The results presented at the conference revealed a delayed-onset antidepressant profile that was notably distinct from findings in major depression studies. Depression rating scale scores showed no immediate post-infusion group differences at the forty-minute time point, with therapeutic effects emerging at twenty-four hours and sustained through the two-week follow-up period. This unique temporal profile suggests that ketamine may exert its antidepressant effects through different mechanisms or kinetics in opioid use disorder populations compared to individuals with major depression alone. Preliminary mechanistic analyses examining heart rate variability, stress biomarkers, and synaptic plasticity markers revealed promising patterns that could potentially explain some of the unique temporal profile and sustained efficacy of ketamine in this population. These findings suggest that ketamine’s effects in opioid use disorder may involve distinct neurobiological pathways related to stress regulation, autonomic function, and synaptic remodeling.

The findings from the PROUD study suggest that ketamine may offer a novel therapeutic approach for treatment-resistant depression in opioid use disorder populations during abstinence maintenance, with a distinct efficacy profile that differs from its effects in primary depression. The delayed but sustained antidepressant response observed in the study has important implications for clinical implementation, suggesting that patients and clinicians should anticipate a different time course of therapeutic benefits compared to ketamine treatment for major depression. Ongoing analyses of the comprehensive neurobiological data collected in the study may identify biomarkers predicting treatment response in this vulnerable population, potentially enabling personalized treatment approaches that could optimize outcomes for individuals at highest risk of relapse during the challenging abstinence maintenance phase. This work represents a significant advance in addressing the unmet clinical need for effective treatments targeting the intersection of addiction and mental health disorders.